1. Field of the Invention
This invention relates to fans for moving a cooling fluid in heat exchange relationship with a contained fluid. More particularly, it relates to axial flow fans for use on variable speed engines for pulling a cooling fluid, such as air, past a cooling coil, such as a radiator, responsive to rotation of a rotary part driven by the engine; the fan effecting flow of air at low speeds, yet reducing normal parasitic load and noise level on the engine at high speeds when sufficient flow passes the radiator of its own volition.
2. Description of the Prior Art
In the early stages of automotive development, construction of fans was very simple because high speeds were not attained and fan design was merely one of the minor considerations in the overall design of a "horseless carriage." With the advent of high speed automobiles and high speed automobile engines; and, particularly, with truck engines; the need for reducing the parasitic power consumption and noise of a fan at high speeds became apparent. At high speeds, the speed of the air with respect to the radiator was adequate to effect most of the desired cooling. The initial approach in this direction was that of decoupling the fan from the engine. Decoupling was effected by a variety of devices; such as, electric or magnetic clutches; operated in response to a thermally responsive element or manual control, and fluidic clutches operated responsive to temperature effects on the rheological properties of the coupling fluids. Typical of the patents relating to this area are U.S. Pat. No. Re. 25,481; 3,191,733; and 3,490,686. Another approach that was employed to effect a reduced power consumption and lower noise by the fan at high speed was the use of flexible blades on the fan, alone or in conjunction with a decoupling device. Typical patents pertinent to the flexible blade structure are U.S. Pat. No. 3,698,835 and the above noted U.S. Pat. No. 3,490,686, as well as earlier patents. In these latter patents, a tapered arcuate hinge is provided with both edges touching a stiff spider arm in order to allow flexure of the blade, yet still provide stiffness, support and pitch, or angle of attack. Even the latter highly advanced and sophisticated blade, however, have not been found totally satisfactory in that it still requires too high a power consumption and noise level at high speeds, and requires a flexible but strong material, like steel, that is becoming increasingly expensive.
Moreover, all of the available fans have considerable undesirable "tip dance," or erratic movement of blade tips, at the rates of rotation above about 2,000 revolutions per minute (rpm).
From the prior art, it can be seen that no one has designed a fan blade in accordance with known aerodynamic principles for use with an automobile engine. Heretofore, it has been considered too expensive to engage in this approach, as well as the feeling by experts that this approach would not be rewarding, since the air foil so constructed would have too much lift, or forward pull, because of the Bernouli effect on the forward side of the blade. Moreover, a blade made in accordance with the prior art that would withstand the centrifugal forces involved at high speed rotation, assuming it were not disconnected, would be inordinately expensive, requiring forged metallic construction or the like. In addition, it was thought that the air flow that would have to split around the forward edge of the fan blades would be so diverted as to stall the blade because of the high camber of the blade as well as the thickness of the chords of the blade.
Accordingly, it is an object of this invention to provide an axial flow fan having fan blades that obviate the disadvantages of the prior art and provide an axial flow fan that is designed similarly as are supersonic air foils; and, consequently, has exceptionally low power consumption at all speeds, yet effects the desired airflow with unusually low noise and tip dance of the fan, even at high speeds.
It is also an object of this invention to provide a sophisticated method of manufacture and fan that will achieve a highly efficient axial flow fan that provides the foregoing object and yet is easy to manufacture, durable, maintenance free and dependable.
These and other objects will become apparent from the descriptive matter hereinafter, particularly when taken in conjunction with the drawings.